Potentiometer



NDV. 30, 1948. M. LEVY 2,454,816

POTENTIOIETER Filed 001;. 22, 1946 F/GZ 24 7 IL Q Ml J 7 0 \\Q I f WW4 g7.

A llorney Patented Nov. 30, 1948 POTENTIOMETER Maurice Moise Levy, London, England, assignor to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application October 22, 1946, Serial No. 704,972 In Great Britain February 14, 1946 1 Claim.

This invention relates to electrical potentiometers, and its object is to provide a potentiometer having a fine control of tapped resistance.

According to the invention an electrical potentiometer comprises a resistance arranged in spiral form, a contact movable backwards and forwards along the spiral resistance, stationary terminals for both ends of the resistance, and a stationary terminal with which the movable contact is in electrical connection throughout its path of travel to and fro along the spiral reslstance.

The invention will be fully understood from the following description of one embodiment thereof shown in the accompanying drawings in which:

Figure 1 shows a potentiometer in cross-sectional elevation; and

Figure 2 shows detached views in plan and elevation of cursor arm and feeder wiper.

The base of a moulded Bakelite potentiometer l is centrally apertured to receive a spindle 2 to which is fixed a bush 25 with a screw-threaded extension 4. The aperture 2I has a peripheral groove 22 complete except for a locking key 23 which engages a cut-away slot in a flange on the bush 25 seating in the groove 22. The bush and spindle are fixed in the potentiometer I by a hexagon nut 3.

On the spindle 2 above the bush 25 are fixed a Bakelite radial arm 5 and a Bakelite disc 6. The arm 5 carries a cursor I6 engaging a roughly spiral groove II in the base of potentiometer I. The ends of the groove positively limit the maximum possible rotation; about 650, of the arm and the Bakelite disc.

The Bakelite disc 6 carries a spring metal member I constituting a feeder wiper and a cursor-carrier. The member I is shown separately in Figure 2 and comprises a two-armed base portion 26 fixed to the disc 6. Integral with the middle of the base 26 is a long arm I which is bent over radially so as to be spaced from the disc 6 and then doubled under at 21 to rest on the disc to which it is fixed. The two arms of the base 26 also have extensions bent backwards above the base and shaped to engage and wipe over a fixed contact disc I3 fixed in a Bakelite lid 9 for the pot l. A cursor 8 is slidably mounted on the arm I.

The lid 9 rests on a ledge I8 in the pot I and is fixed in position by a fiat spring Ill engaging a groove in the rim of the potentiometer I. The lid is held from rotation by a key I9 on the ledge I8 engaging a slot in the lid.

The underside of lid 9 is formed with a mathly spiral raised track II on which is fixed a carbon resistance strip I2. Terminals I4, I5 (2 separate terminals 15 one of which is not visible in the cross-section) are mounted on the top of the lid 9. The terminal I4 is riveted to the contact disc I3 and the terminals I5 to the ends of the resistance strip I2.

The cursor 8 has upstanding contact arms embracing the raised track II and a nipple on its horizontal face engages the carbon strip I2.

It will be seen that rotation of the spindle rotates the arms 5, I and wiper 24. Rotation of the arm I causes cursor 8 to move along the spiral resistance strip I2, the cursor sliding on the arm I to the extent required by the variation in radial distance of strip I2 from the spindle axis. At the same time, wiper 24 rotates in contact with contact disc I3, so that the cursor 8 is always in electrical connection with terminal I4. Rotation of the arm 5 moves the cursor l 6 along the spiral slot II, within positive limits which define the travel of cursor 8 on the carbon strip I2.

What is claimed is;

An electrical potentiometer of box-like form comprising a spindle mounted axially in the box, a roughly spiral resistance element on the interior surface of one end plate, a roughly spiral guide on the interior surface of the other end plate and furnished with positive end stops, the spindle carrying a rotatable assembly comprising a first radial arm carrying a first cursor cooperating with the spiral resistance strip, a second radial arm carrying a second cursor co-opcrating with the spiral guide, and a wiper electrically connected to the first cursor and wiping over a fixed contact disc plate mounted on the end plate carrying the spiral resistance whereby there is continuous electrical connection between the resistance strip and the fixed contact plate through the first cursor.

MAURICE MOISE LEVY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,320,119 Brown et al Oct. 28, 1919 1,450,919 Harris Apr. 10, 1923 1,785,779 Lauter Dec. 23, 1930 FOREIGN PATENTS Number Country Date 674,383 France Jan. 28, 1930 

